Abstract

AIMS: GHB is produced naturally in the human body and is also a Class C controlled substance under the
Misuse of Drugs Act 1971. It is notorious because of its association with drug facilitated sexual assaults
(DFSA). Studies have indicated that large variations in urinary and blood concentrations of endogenous
GHB occur across population groups (1). At present the recognised cut off values of 10 µg/mL in urine and
5 µg/mL in blood may only provide reliable evidence if the sample was taken <12 hours after ingestion
because GHB is rapidly metabolised and excreted from the body (2).
A recent study, using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS),
found a significant difference (> 13.5%) in the values of ∂13C found in endogenous GHB in five
postmortem blood samples (range: 13.8 - 86.3 µg/mL) compared to synthetically produced GHB with
the implication that stable isotope measurements could significantly increase time frames of detection
in reported DFSA (3). The aim of this study is to determine the ∂13C values of GHB at concentrations below
the recognised cut off values in urine samples.
METHODS: GHB can be derivatised or converted to gamma-butyrolactone (GBL) for GC analysis. We
have derivatised GHB using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1%
trimethylchlorosilane (TMCS) (linear response: 0.05 - 25 µg/mL), and converted GHB to GBL (linear
response: 0.5 - 50 µg/mL) based upon on a method developed ‘in-house’ by the Forensic Science
Service Ltd.
RESULTS AND CONCLUSIONS: Preliminary ∂13C (%) values for synthetic GBL at 50 µg/mL (mean -26.5%;
σn-1 0.06; n = 3) and GHB-TMS derivatives at 200 µg/mL (mean -34.2%; σn-1 0.21; n = 3) have been
obtained using a Thermo Finnigan MAT 253 IR-MS coupled to a Trace Ultra GC/Combustion III Interface.
However, we found that extraction of GHB from urine using solid phase extraction (CLEAN SCREEN®
GHB and Oasis® MAX cartridges) did not remove interfering compounds sufficiently to be able to
precisely determine ∂13C values at levels less than 10 µg/mL. Therefore, we propose synthesising an
immunising antigen to make an antibody to specifically target GHB using immunoaffinity column
extraction.